1. Field of the Invention
This invention relates to a zoom optical system and an electronic pickup apparatus using the same.
2. Description of the Related Art
In recent years, it has been known that compact cameras which are designed to become thin include a compact camera in which an optical system is retracted to be stored in the camera housing in a state in which photography is not performed. In order to make such a compact camera more thinner, the thickness within which the optical system is retracted has to be made to become thin.
Now, it is known that constitutions for retracting an optical system include a constitution in which a lens frame for holding the optical system is divided into a plurality of parts so that the lens frame can expand and contract. However, such a constitution requires the large number of the parts into which the lens frame is divided, in order to make a thin thickness for retracting the optical system. As a result, the weight of the whole of the lens frame becomes large, and the divided parts of the lens frame are hard to arrange on the same axis in a state in which the lens frame is not retracted, so that eccentricity is easy to cause in the optical system. Accordingly, in the case where such a constitution is adopted, it is required that the interval at which the lens frame is divided into a plurality of parts is shortened while the number of parts into which the lens frame is divided is being decreased.
And, it is preferred that the total length of the optical system is shortened in both states of the optical system retracting and not retracting, in order to meet these demands. Such optical system is described, for example, in Japanese Patent Kokai No. 2007-271711. The optical system that is described in Japanese Patent Kokai No. 2007-271711 is formed in such a way that the first lens group on the most object side is formed by a cemented lens which is composed of a negative lens and a positive lens. As a result, the first lens group is made to become thin with the occurrence of chromatic aberration restrained.